Edit Collateral

Selecting the Edit Collateral option from the 3 dots menu on the Positions table will bring up this pop-up window allowing you to either deposit or withdraw from your position's current collateral.

Withdrawing collateral will result in a tighter liquidation price but can free up the collateral for other positions if desired. On the other hand, depositing collateral will decrease leverage and thus push out the liquidation price if that is a concern.